The present invention relates to a bucket of a stage of a gas turbine and particularly relates to a second stage turbine bucket internal core profile.
Many system requirements must be met for each stage of the hot gas path section of a gas turbine in order to meet design goals including overall improved efficiency and airfoil loading. Particularly, the buckets of the second stage of the turbine section must meet the operating requirements for that particular stage and also meet requirements for bucket cooling area and wall thickness. Internal cooling requirements must be optimized, necessitating a unique internal core profile to meet stage performance requirements enabling the turbine to operate in a safe, efficient and smooth manner.
In accordance with a preferred embodiment of the present invention there is provided a unique internal core profile for a bucket of a gas turbine, preferably the second stage bucket, that enhances the performance of the gas turbine. It will be appreciated that the external airfoil shape of the second stage bucket airfoil improves the interaction between various stages of the turbine, and affords improved aerodynamic efficiency and mechanical loading. The external airfoil profile for the preferred bucket is set forth in a companion patent application Ser. No. 10/320,655, filed Dec. 17, 2002, titled xe2x80x9cAirfoil Shape for a Turbine Bucketxe2x80x9d, the disclosure of which is incorporated by reference. Concomitantly, the internal core shape is also significant for structural reasons as well as to optimize internal cooling with appropriate wall thickness.
The bucket internal core profile is defined by a unique loci of points which achieves the necessary structural and cooling requirements whereby improved turbine performance is obtained. This unique loci of points define the internal nominal core profile and are identified by the X, Y and Z Cartesian coordinates of Table I which follows. The 3700 points for the coordinate values shown in Table I are for a cold, i.e., room temperature bucket at various cross-sections of the bucket airfoil along its length. The positive X, Y and Z directions are axial toward the exhaust end of the turbine, tangential in the direction of engine rotation looking aft and radially outwardly toward the bucket tip, respectively. The X and Y coordinates are given, in distance dimensions, e.g., units of inches, and are joined smoothly at each Z location to form a smooth continuous internal core profile cross-section. The Z coordinates are given in non-dimensionalized form from 0 to 1. By multiplying the bucket height dimension, e.g., in inches, by the non-dimensional Z value of Table I, the internal core profile, of the bucket is obtained. Each defined internal core profile section in the X, Y plane is joined smoothly with adjacent profile sections in the z direction to form the complete internal bucket core profile.
The preferred second stage turbine bucket includes side wall surfaces with ribs extending internally between and formed integrally with the side walls. The ribs are spaced from one another and define with internal wall surfaces of the bucket side walls internal cooling passages, preferably serpentine in configuration, along the length of the bucket. The smooth continuing arcs or lines extending between the X, Y coordinates to define each profile section at each distance Z extend along the internal wall surfaces of the cooling passages and between adjacent passages along each of the side walls. Consequently, each internal core profile section has envelope portions which pass through the juncture between the ribs and each of the side walls as well as along the side walls of the cooling passages. These internal core profile sections are generally airfoil in shape at least in the airfoil portion of the bucket.
It will be appreciated that as each bucket heats up in use, the internal core profile will change as a result of mechanical loading and temperature. Thus, the cold or room temperature profile is given by the X, Y and Z coordinates for manufacturing purposes. Because a manufactured internal bucket core profile may be different from the nominal profile given by the following table, a distance of plus or minus 0.039 inches from the nominal profile in a direction normal to any surface location along the nominal profile defines a profile envelope for this internal bucket core profile. The profile is robust to this variation without impairment of the mechanical, cooling and aerodynamic functions of the bucket.
It will also be appreciated that the bucket can be scaled up or scaled down geometrically for introduction into similar turbine designs. Consequently, the X and Y coordinates in inches and the non-dimensional Z coordinates, when converted to inches, of the internal nominal core profile given below may be a function of the same constant or number. That is, the X, Y and Z coordinate values in inches may be multiplied or divided by the same constant or number to provide a scaled up or scaled down version of the internal bucket core profile while retaining the core profile section shape.
In a preferred embodiment according to the present invention, there is provided a turbine bucket including an airfoil, a platform, a shank and a dovetail having an internal nominal core profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0 to 1 convertible to Z distances in inches by multiplying the Z values by a height of the bucket in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define internal core profile sections at each distance Z along the bucket, the profile sections at the Z distances being joined smoothly with one another to form the bucket internal core profile.
In a further preferred embodiment according to the present invention, there is provided a turbine bucket including an airfoil, a platform, a shank and a dovetail, the bucket having an internal nominal core profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0 to 1 convertible to Z distances in inches by multiplying the Z values by a height of the bucket in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define internal core profile sections at each Z distance along the bucket, the profile sections at the Z distances being joined smoothly with one another to form the bucket internal core profile, the X, Y and Z distances being scalable as a function of the same constant or number to provide a scaled-up or scaled-down internal core profile.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine wheel having a plurality of buckets, each of the buckets including an airfoil, a platform, a shank and a dovetail, each bucket having an internal nominal core profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0 to 1 convertible to Z distances in inches by multiplying the Z values by a height of the bucket in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define internal core profile sections at each distance Z along the bucket, the profile sections at the Z distances being joined smoothly with one another to form the bucket internal core profile.